The present invention relates to a process and apparatus for producing iron carbide.
A traditional method for producing steel from iron oxide such as iron ore normally comprises the steps of;
in the first step, producing molten pig iron in such a manner that coke produced at a coke oven, other raw materials and iron oxide are charged into a blast furnace, and thereafter, iron oxide are molten and reduced by combustion heat of carbon contained in coke generated due to blowing of high temperature oxygen and carbon monoxide generated due to combustion of said carbon;
in the second step, charging the molten pig iron into a converter, and converting the molten pig iron by oxygen blowing into steel, wherein a carbon concentration of which is under the demanded value.
Since such traditional steel making process by a blast furnace requires many ancillary facilities such as coke oven, sintering furnace, and air-heating furnace, equipment cost becomes high. Furthermore, this steel making process via a blast furnace requires the expensive coal such as high coking coal and huge site for many facilities and raw materials storage. Therefore, recently, to overcome the above disadvantages of using a blast furnace, new iron making processes, instead of a blast furnace, have been developed and put to practical use.
For example, one of the newly developed processes for producing steel is a method called as iron carbide-electric furnace process. This process comprises the steps of obtaining iron carbide by reacting grainy iron oxide with a reducing agent such as hydrogen and a carburizing agent such as methane gas, and producing steel by smelting said iron carbide at an electric furnace. A fluidized bed reactor is a well known apparatus for producing iron carbide. The laid open publication No. HEI 6-501983, which is the publication of the Japanese translation of International Patent Application No. PCT/US91/05198 discloses an apparatus for producing iron carbide. As shown in FIG. 8, said publication shows an apparatus for producing iron carbide, wherein when a grainy iron oxide is charged into fluidized bed reactor 32 via inlet 31, the grainy iron oxide is reduced under floating and fluidizing due to the high temperature and high pressure gas being introduced from multiple nozzles 33 located in the bottom portion of the reactor. Thereafter, the iron oxide is broken into smaller pieces as a result of the foregoing reaction and moves along with a passage formed by baffle-plates 34, 35, 36, 37, and is finally discharged as iron carbide from outlet 38. (Hereinafter, this apparatus is called as prior art.)
By the way, the reaction for converting iron oxide into iron carbide proceeds as shown in the following formulas (1) through (6).
(1) Fe2O3+3H2xe2x86x922Fe+3H2O (FeO1.5+1.5H2xe2x86x92Fe+1.5H2O) 
(2) Fe3O4+4H2xe2x86x923Fe+4H2O (FeO1.3+1.3H2xe2x86x92Fe+1.3H2O) 
(3) Fe3O4+H2xe2x86x923FeO+H2O 
(4) FeO+H2xe2x86x92Fe+H2O 
(5) 3Fe+CH4xe2x86x92Fe3C+2H2 
(6) 3Fe2O3+5H2+2CH4xe2x86x922Fe3C+9H2O 
As shown in the above formulas (1) through (6), the iron oxide is converted into iron carbide in turn of Fe2O3, Fe3O4, FeO, Fe and Fe3C, and the volume of the reducing gas H2 to be used varies according to each stage in the reducing reaction. On the other hand, under some gas temperature or some gas composition, there is such a case that FeO is not generated. As is described below, the prior art has the various problems to be solved.
First, the higher the concentration of methane and carbon monoxide contained in the reducing and carburizing gas becomes, the faster the carburizing reaction proceeds. But when the concentration of methane and carbon monoxide contained in said reaction gas becomes excessively high, a fixed carbon is generated from the reaction gas due to the reaction as shown in the following formulas (7) and/or (8).
As a result, extra reaction gas is uselessly consumed. Furthermore, the fixed carbon has such a bad effect upon the gas circulation loop as to be turned into dust and sticked on a tube of gas heater.
(7) CH4xe2x86x92C(fixed carbon)+2H2 
(8) 2COxe2x86x92C(fixed carbon)+CO2 
At the most vigorous stage of the reaction, the reducing reaction by hydrogen is conducted vigorously as is described above, and the water vapor generated by said reducing reaction prevent the generation of fixed carbon. But, at the final stage of the reaction, since little water vapor for preventing the generation of fixed carbon is generated, the fixed carbon is liable to easily generate. There are two means to prevent the generation of fixed carbon. One is to decrease the concentration of methane and carbon monoxide contained in the reaction gas, and the other is to increase the concentration of water vapor contained in the reaction gas. But those means result in the decline of the reaction speed, namely, the lowering of the productivity.
The higher the gas temperature becomes, the faster the reaction speed becomes. But, when the temperature of the fluidized bed comes to be over about 600xc2x0 C. (for example, 570xc2x0 C.xcx9c590xc2x0 C.) due to the excessively high temperature gas, the iron oxide remained in the product of iron carbide is turned into not Fe3O4 whose chemical character is stable, but FeO whose chemical character is unstable.
If the reaction gas temperature is decreased so as to avoid the above disadvantage, it will result in the decline of the reaction speed, namely, the lowering of the productivity.
Furthermore, as the reaction proceeds, the specific gravity of iron oxide becomes lower and the diameter of iron oxide particles become smaller due to its own powdering. Therefore, the iron oxide particles at the stage of the second half of the reaction is liable to fly. The iron oxide particles flown outside the reactor has the low carburization degree because of the short staying time at the reactor. As a result, it brings the lowering of the average carburization degree of the product of iron carbide.
Consequently, it is preferable to regulate the flow velocity of the gas flowing through the fluidized bed according to the proceeding of the reaction. But it is impossible for the prior art to change the flow velocity of the gas, unless applying some complicated works, such as alternating the resistance of the gas blowing nozzle installed at the gas distribution plate.
Furthermore the method for producing iron carbide, which is characterized by that the reducing reaction is partially conducted in a first stage reactor, then the further reducing and carburizing reaction is conducted in a second stage reactor, is known.
But in this method, the control of reduction degree of the ore discharged from the first stage reactor is necessary. It is possible to control the reduction degree by altering the gas flow rate, the gas temperature or the gas composition. Said altering, however, is not easy because the quantity of gas to deal with is so much. As a result, it presents the difficulty in controlling conformably and carefully the reduction degree.
The above-mentioned disadvantages of the prior art for producing iron carbide will be easily overcome by the present invention.
The objective of the present invention is to provide a process and apparatus for producing effectively iron carbide having the chemically stable components.
An object of this invention is to provide a process for producing iron carbide by an apparatus having constitution elements (a) to (e);
(a) a fluidized bed located at an upper part within a fludized bed reactor, and,
(b) a chamber located at a lower part within the reactor to work as a gas header for introducing a reducing and carburizing gas; wherein the fluidized bed and the chamber are separated into upside and downside by a distribution plate on which multiple gas introducing nozzles are installed; and the fluidized bed located at an upper part of the distribution plate is partitioned into plural division rooms which are formed in isolated or mazy room by a partition plate; and,
(c) plural gas supply inlets arranged on the chamber for supplying gas respectively to the specific division room, and, connecting a gas supply line to each gas supply inlet in order to supply a reducing and carburizing gas, wherein each gas supply line has a gas flow control valve which controls gas pressure or gas flow rate; and,
(d) one or more than two of gas circulation loop having a quenching tower and a cooler which eliminate dusts contained in the exhaust gas and reduce water vapor contained in the exhaust gas, and having a preheater for heating the gas, wherein the exhaust gas is returned to the chamber by way of the quenching tower, cooler and preheater; and,
(e) a gas supplying apparatus through which hydrogen gas and carbon-containing gas such as methane are supplied to a gas circulation loop; and further, comprising steps for reacting grainy iron oxide charged from a side wall of the reactor with the gas in such a manner that;
the iron oxide is floated and fluidized by high temperature and high pressure gas being introduced form the bottom portion of the reactor, and then, transferred from the division room of the upstream side to the division room of the downstream side via a communication space which may locate at either upper or lower part of said partition plate, and finally, produced iron carbide is discharged from the final division room.
Another object of the present invention is to provide a process for producing iron carbide, wherein a chamber is separated into plural parts by separation plate and each separated part comprises an individual gas supply inlet respectively.
Another object of the present invention is to provide a process for producing iron carbide, wherein a separation plate is installed at the upper part of the chamber in such a manner that only the upper part of the chamber is divided into plural parts by said separation plate.
Another object of the present invention is to provide a process for producing iron carbide, wherein a separation plate is installed from the top of the chamber to the bottom thereof for isolating each separation part.
Another object of the present invention is to provide a process for producing iron carbide, wherein a separation plate is installed from the top of the chamber to the bottom thereof for separating the chamber into plural parts, and the separated parts are communicated each other via an aperture arranged on the separation plate.
Another object of the present invention is to provide a process for producing iron carbide wherein the amount of water vapor contained in the gas to be supplied to the division room of the downstream side is made larger than that contained in the gas to be supplied to the division room of the upstream side.
Another object of the present invention is to provide a process for producing iron carbide, wherein the amount of water vapor contained in the gas to be supplied to the division room of the downstream side is increased by supplying water vapor from the outside of the reactor.
Another object of the present invention is to provide a process for producing iron carbide, wherein the amount of water vapor contained in the gas to be supplied to the division room of the downstream side is increased in such a manner that cooling operation of a quenching tower and a cooler in a gas circulation loop is regulated so as to decrease the amount of removal of water vapor by said quenching tower and said cooler.
Another object of the present invention is to provide a process for producing iron carbide, wherein the hydrocarbon gas or the carbon monoxide gas contained in the gas to be supplied to the division room of the downstream side is made smaller than that contained in the gas to be supplied to the division room of the upstream side.
Another object of the present invention is to provide a process for producing iron carbide, wherein the amount of the hydrocarbon gas or the carbon monoxide gas contained in the gas to be supplied to the division room of the upstream side is increased by supplying hydrocarbon gas or carbon monoxide gas from the outside of the reactor more than that contained in the gas to be supplied to the division room of the downstream side.
Another object of the present invention is to provide a process for producing iron carbide, wherein the gas flow rate per unit area of the gas to be supplied to the division room of the downstream side is made smaller than that of the gas to be supplied to the division room of the upstream side.
Another object of the present invention is to provide a process for producing iron carbide, wherein the temperature of the gas to be supplied to the division room of the downstream side is made lower than that of the gas to be supplied to the division room of the upstream side.
Another object of the present invention is to provide a process for producing iron carbide, wherein the temperature of the gas to be supplied to the division room of the downstream side is made lower than that of the gas to be supplied to the division room of the upstream side in such a manner that a low temperature gas is mixed with the gas discharged from the preheater in the gas circulation loop.
Another object of the present invention is to provide a process for producing iron carbide, wherein the low temperature gas is a part of the gas to be supplied to a preheater.
Another object of the present invention is to provide a process for producing iron carbide, wherein the low temperature gas is supplied from the outside of the reactor.
Another object of the present invention is to provide a process for producing iron carbide, wherein the temperature of the fluidized bed in the division room of the downstream side is made in the range of 500xcx9c600xc2x0 C.
Another object of the present invention is to provide a process for producing iron carbide, wherein the temperature of the fluidized bed in the last division room of the downstream side is made in the range of 500xcx9c600xc2x0 C. by decreasing the temperature of only the gas to be supplied to the last division room of the downstream side.
Another object of the present invention is to provide a process for producing iron carbide, wherein the temperature of the gas to be supplied to the division room of the downstream side is made lower than that of the gas to be supplied to the division room of the upstream side in such a manner that oxygen is mixed with the gas to be supplied to division room of the upstream side, and then, a part of combustible gas contained in said gas is partially burned in order to raise the gas temperature.
Another object of the present invention is to provide a process for producing iron carbide, wherein the concentration of hydrogen contained in the gas to be supplied to the division room of the upstream side is made higher than that of hydrogen contained in the gas to be supplied to the division room of the downstream side.
A still further object of the present invention is to provide a process for producing iron carbide, wherein the concentration of the hydrogen in the gas to be supplied to the division room of the upstream side is increased by supplying hydrogen gas from the outside of the reactor.
Another aspect of this invention is to provide an apparatus for producing iron carbide comprising the constitution elements (a) to (e);
(a) a fluidized bed located at an upper part within a fludized bed reactor, and,
(b) a chamber located at a lower part within the reactor to work as a gas header for introducing a reducing and carburizing gas; wherein the fluidized bed and the chamber are separated into upside and downside by a distribution plate on which multiple gas introducing nozzles are installed; and the fluidized bed located at an upper part of the distribution plate is partitioned into plural division rooms which are formed in isolated or mazy room by partition plate; and,
(c) plural gas supply inlets arranged on the chamber for supplying gas respectively to the specific division room; and, connecting a gas supply line to each gas supply inlet in order to supply a reducing and carburizing gas; wherein each gas supply line has a gas flow control valve which controls each gas pressure or gas flow rate; and,
(d) one or more than two of gas circulation loop having a quenching tower and a cooler which eliminate dusts contained in the exhaust gas and reduce water vapor contained in the exhaust gas, and having a preheater for heating the gas, wherein the exhaust gas is returned to the chamber by way of the quenching tower, cooler and preheater; and,
(e) a gas supplying apparatus through which hydrogen and carbon- containing gas such as methane are supplied to said gas circulation loop.
H2, CH4, CO, CO2 and H2O and the like can be used as a reaction gas for the present invention.
The present process and apparatus for producing iron carbide having the above constructions demonstrates the following advantages.
That is to say, it can be conducted by the present invention that the gas conditions such as gas temperature, gas flow rate and gas composition, which is introduced into the fluidized bed of iron oxide particle inside the reactor, may not make fixed but partially changed.
Consequently, it is possible to lower the concentration of methane and carbon monoxide and raise the concentration of water vapor contained in the gas introduced into the division room of the downstream side in comparison with the concentration of those gases contained in gas introduced into the division room of the upstream side. It thus can be achieved to maintain a high productivity operation under preventing the generation of fixed carbon from the reaction gas.
It is possible to lower the gas temperature introduced into the division room of the downstream side in comparison with the gas temperature introduced into the division room of the upstream side. It thus can be achieved to maintain a high productivity operation and produce iron carbide having a small quantity of chemically unstable wustite and a large quantity of chemically stable magnetite.
Furthermore, it is possible to decrease the gas flow rate introduced into the division room of the downstream side in comparison with the gas flow rate introduced into the division room of the upstream side according to the decreasing specific gravity and particle diameter in accordance with the proceeding of the reaction. It thus can be achieved to decrease the iron oxide flown the outside the reactor and produce iron carbide having a high average carburization ratio.
In case of conducting the reducing and carburizing reaction using two reactors, it is easy to alter the gas flow rate, the gas composition and/or the gas temperature because the gas quantity introduced into the division room of the fluidized bed at the final reaction stage of the first reactor is smaller than the whole gas quantity. It thus can easily be achieved to control the reduction degree of iron oxide including metallic iron discharged from the first reactor.
Furthermore, by the present invention, it can be accomplished to prevent the generation of fixed carbon from the reducing and carburizing gas and allow the kind of iron oxide remaining in the product of iron carbide to be magnetite whose chemical character is stable. It also can be accomplished to decrease the quantity of iron ore particle flown outside the reactor.
As a result, the present invention can provide a process and apparatus for producing effectively iron carbide with the high operation ratio and the low production cost.